Salles has displayed his filmmaking chops in (among others) “Central Station” and “Motorcycle Diaries.” It's harder to criticize his specific choices in “On the Road” than to criticize his decision to take on the project in the first place. No superior suggestions for how to film it leap to mind: Perhaps Salles has given us the best possible take on the material, and that take still isn't good enough.

For those younger types to whom the name Kerouac is only vaguely familiar (if familiar at all), the author was a lower-middle-class Catholic, grew up in Massachusetts, briefly went to Columbia on a football scholarship, even more briefly served in the Navy, and then, in the post-war years, hung around with a group of writers and artists who a few decades earlier would have been known as “Bohemian,” but ended up being known as “the Beat Generation” (or, more popularly, “beatniks”). His writing career was up and down before the 1958 publication of “On the Road” — a thinly veiled account of his experiences in the late '40s. Friends like William S. Burroughs and Allen Ginsberg appear under different names.

The '60s notion of “drugs, sex, and rock 'n' roll” might have applied to their lifestyle, except rock ‘n' roll hadn't been invented yet, so call it “sex, drugs and jazz.” Salles wisely downplays the oft-noted role of beatniks as forerunners to the hippies of the '60s, but the latter can't be wholly explained as a simple progression from the former. Ginsberg was the only one to be equally involved in both phenomena; by the time Kerouac died from alcoholism in 1969, he was living with his mother and mumbling right-wing screeds.

The movie follows the book surprisingly closely. This may be its strongest virtue and its obituary. The book is episodic and rambling, the narrator's various journeys only held together by a yearning for ... something. It's the sort of rambling that often grows tiresome on screen: Prose can get away with certain characteristics that translate poorly into a structured drama. But imposing more structure (as in the 1980 Kerouac-themed movie “Heart Beat”) would have destroyed the tone.

The casting of the three main characters is also a problem. Much of the drive in the novel stems from Kerouac's fascination (or even bromance) with his friend Neal Cassady (here named Dean Moriarty). As Moriarty, Garrett Hedlund simply can't generate sufficient charisma to lure us into sharing Kerouac's perspective. Sam Riley, playing Sal Paradise, the Kerouac figure, leaves little impression. And Kristen Stewart, as the most prominent of their female friends ... well, she'd better hope there are more teen romance roles waiting for her, because here she's simply lousy.

Kirsten Dunst fares infinitely better in the other main female role. And Viggo Mortensen (as the Burroughs surrogate) does an uncanny job of reproducing Burroughs' well-known voice, while capturing the whole of the character as well as (or better than) Peter Weller in “Naked Lunch.” Very little of the book's humor comes across on screen, and Mortensen manages to provide what little there is.

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ANDY KLEINis the film critic for Marquee. He can also be heard on “FilmWeek” on KPCC-FM (89.3).